Distubance approaching the Caribbean grows stronger

A tropical wave near 11N 55W, about 400 miles east of the southernmost Lesser Antilles Islands, is moving westward towards the Caribbean at about 20 mph. Thunderstorm activity has increased markedly today in association with this wave (labeled 97L by NHC), and it has the potential to develop into a tropical depression by Thursday. The Hurricane Hunters are tasked to investigate it on Thursday afternoon. The thunderstorm activity is still pretty disorganized, and mostly lies to the west of the center of circulation, so noon Thursday is the earliest it is likely to reach tropical depression status.

Wind shear is favorable, a low 5-10 knots, but is a very high 30-40 knots just to the north, and any movement of this high shear zone to the south--or 97L to the north--might disrupt it. A large area of dry air and Saharan dust lies to the north, and this has slowed development today. The storm will spread heavy rains and wind gusts to 40 mph across Trinidad, Tobago, Grenada, and the South American coast of Venezuela on Thursday, and the ABC Islands of Aruba, Bonaire, and Curacao on Friday. Development into a tropical depression--or a tropical storm--is highly dependent on how close 97L comes to the coast of Venezuela. The southeast Caribbean off the Venezuelan coast has been climatologically unfriendly to developing tropical storms. The presence of the South American land mass so close cuts off a key source of moisture for a developing storm, and many vigorous looking disturbances and tropical storms have died here.

The computer models' take on thingsThe latest 8am EDT computer model runs are in. The Canadian model continues to be gung-ho, developing 97L into a strong tropical storm on Saturday, south of Jamaica. The NOGAPS model assumes a more southerly track will occur, and develops 97L Saturday once it moves off the coast of Columbia. NOGAPS then takes a weak storm along the north coast of Honduras, then across the Yucatan and into the Gulf of Mexico. The GFS assumes the storm will move further north than is reasonable, and does not develop it. I think the GFS solution can be discounted. The UKMET takes the storm along the north coast of South America, and does not develop it.

My take on thingsI believe there's about a 60% chance 97L will become a tropical storm. It should come very close to developing into a tropical depression Thursday afternoon or evening. However, its close proximity to South America will probably keep it somewhere between a near-tropical depression and a 45-mph tropical storm until Saturday. If it survives into Saturday, intensification into a strong tropical storm or hurricane in the western Caribbean is possible. There may be additional obstacles to overcome by then--such as too much wind shear, or the Yucatan Peninsula or Honduras getting in its way.

DebbyTropical Storm Debby has deteriorated a bit this afternoon, thanks to dry air and cooler waters. Debby is expected to turn more northwestward over the weekend, and get pulled northwards and recurved into the prevailing westerly winds at high latitudes over cold waters early next week. Debby is not a threat to any land areas. The storm will be in a more favorable environment for intensification on Friday, and could eventually make it to Category 2 hurricane status, as predicted by the GFDL model.

I have watched long enough to understand the general biases of the models, and to learn that most do not accurately predict path until a system has existed for a day or two. None seem very good at predicting cyclogenesis.

Are there any models which focus solely on cyclogenesis, and do not worry about future intensity and track? It would seem that accurate prediction of deep convection and localized interactions that affect development of closed circulation at the surface would be valuable, and could then better seed the existing models. It seems like "we" have pretty good ideas of where to look, but we have to wait until a circulation pops out to say much.

I think we're all gonna go batty right now with these models. The fact that the GFDL went from CAT2 to dissipation shows us the models are having fits right now trying to initialize this. It will take several more runs before they start getting a grip.

Posted By: Weather456 at 11:55 AM GMT on August 24, 2006.guygee, that was from yesterday.....SLU posted a pick just like that last night....and 97L is already near Barbados and that pass shows where it was last night.

Weather456 - Your are correct. The same link now shows at the top 12:07 UTC, but the actual data is unchanged. I finally figured out it is the small number below the image in violet that shows the time of the swath intersect with 20N.

There's some dry air creeping around 97L to north and even west a bit. But new flare ups are starting to show. Looks like strong shear ahead to the west. Dry air and shear. Let's see if this system can dodge those 2 bullets this time and be our 1st hurricane (unless Debby intensifies). Wonder if the shear in E caribb will dissipate in time.

i can see where the southern component of 97l skirts the SA coast, emerges west.....

the northern portion could take a more wnw track.....

ok, seems unlikely to me that we will get "2" storms, but at this point, i couldnt tell you which part, upper or lower, will prevail, if at all.....

if i had to guess..... the lower portin may fizzle somewhat due to interaction with SA, which allows the upper portion to be more free of the interaction with the southern portion, which to me at this point, seems to be inhibiting the upper portions development.

i think he "upper" portion could have a shot at the east coast....

this is not wishcasting, just trying to throw out possibilities.....

and there is also the possibility (large) that i don't know what the hades i am talking about! LOL

I really think the NHC is being so bullish about development today, because they want the news people to start paying attention. Which I have no problem with. As far as for the shear it is weakening some and should continue to do so. I don't think 97L will dissipate but it will be setback.

BTW..That trough coming through the Northern Gulf is beginning to eat into the UUL in the Gulf..........It may be history by this time tommorow...............Im also off to work and will check back this afternoon......

It seems the difference between 97l and most of the other Atlantic systems that died so far this year is that it has a lot of moisture to build convection with. That may be enough to keep it alive through the shear over the next 24 hours or so. Chris didn't have that moisture and just dissipated when shear increased. I agree today will tell a lot of the story on what will happen. The NHC is certainly leaning toward some developement.